Lignocellulosic materials are widely abundant sparking considerable interest in these materials for various biofuel applications. Lignocellulosic biomass such as wood waste, crop stalks and grasses are potentially sustainable sources of biomass for ethanol production. With most of the terrestrial biomass on earth being lignocellulosic, producing ethanol from lignocellulosic material has the potential to replace up to 30% of annual petroleum consumption in the United States while significantly reducing greenhouse gas emissions. Moreover, the use of lignocellulosic material in ethanol production does not encounter food production pressures as with other crop sources for ethanol such as corn.
Nevertheless, the abundant sugars contained in lignocellulosic materials are blocked from traditional ethanol-producing fermentation reactions because they typically occur in a complex polymerization of lignin and celluloses that is difficult to hydrolyze into soluble sugars for fermentation. Since lignin is highly resistant to water penetration and enzymatic breakdown, it represents a significant barrier to isolating cellulose and other sugars for use in production of both paper and ethanol biofuel. Similarly, the high degree of polymerization of cellulose in woody biomass is also a significant barrier to efficient biofuel conversion and requires chemical and/or enzymatic hydrolysis to produce soluble sugars for fermentation.
Current methods using chemical and enzymatic processes for lignin removal and cellulose hydrolysis are cost prohibitive and inefficient to support industrial-scale lignocellulosic ethanol production. Such chemical and enzymatic processes include harsh liquid-phase acid or base-catalyzed pretreatments aimed at making the cellulose more accessible to enzymatic hydrolysis. These chemical treatments additionally require specialized facilities for safely handling and disposing of hazardous chemicals, resulting in increased costs and environmental concerns. Furthermore, current enzymatic cellulose hydrolysis processes use expensive extracted and purified cellulase enzymes applied to the lignocellulosic biomass in liquid-phase batches. As a result of these significant processing drawbacks, commercially viable ethanol production from lignocellulosic materials remains unrealized.